Optical encoders are conventionally used as motion detectors in applications such as closed-loop feedback control in a motor control system. A typical optical encoder has a light emitter, an encoder disk with a plurality of apertures and a light detector (e.g. photodetectors.) In optical encoder systems, a reticle may be disposed between the light emitter and the light detector to modify the pattern and size of the light projected on the light detector. A reticle is typically used for adjusting a spatial resolution requirement for the encoder system. Smaller reticles may produce output signals having increased spatial resolution than those generated using the larger reticles.
In general, an optical encoder works by emitting a collimated light beam towards the encoder disk. The light beam is interrupted by the encoder disk, as the encoder disk moves. Portions of the collimated light beam project through the apertures onto the photodetectors. As the encoder disk moves, light patterns falling on the photodetectors change. The photodetectors detect these light patterns to generate corresponding output signals, which can be processed to produce digital waveforms. Such digital waveforms of the output signals can be subsequently translated to motion information, for example, a position or a velocity of a motor.
While optical encoder systems can be effective, encoder systems are still prone to undesired variations in output signal offsets, which may be caused by misalignment of components inside the encoder system. For example, signal offsets may be caused by misalignment of the reticle position, in relation to the light emitter and the light detector. In addition, there may be undesired signal offsets, due to errors occurring during the manufacture of the optical encoder. For example, there may be a misalignment in placement of the photodetectors. Further, there may be wobbling of the encoder disk. Additionally, there may be non-uniformity of a light spot of the light emitter. The foregoing may offset the output signal generated by the encoder system.